Making correct exposures is key to successful photography. Getting a well exposed image means that the correct amount of light is reaching the sensor. You might ask: what is the correct amount of light? When do I know my exposure was correct?
Ansel Adams, an old master of landscape photography, wrote many pages about the correct exposure. He was the first human being figuring out how to capture the rising moon and a village at the same time, without the moon being over- or the village being underexposed.
Ansel Adams: Moonrise Hernandez, New Mexico.
Tip 1 - Studying the old masters will always improve your photography.
Some might think, what’s so special about this photo? He can easily have photoshopped it. Well, it was taken in 1941, 50 years before the rise of the internet and digital methods. Quite an astonishing discovery by Adams considering that, by the time he did that shot, photography already existed a 100 years!
So what is the correct amount of light? Finding the correct exposure means finding the right balance between the very dark and the very bright parts of an image. What you always should try to achieve is having an image were the dark parts (called the shadows) and the very bright parts (the highlights) both still show details.
Tip 2 - Analyze your images under the aspect of brightness!
Over- and underexposed pictures.
Let me exemplify further. The following three images show a man I photographed in Cuba.
The left image would be what is called „underexposed“ in terms of photography. The all in all impression is too dark, you hardly can recognise the man’s eyes, the details in the shadows are lost.
The image in the center is correctly exposed. The overall impression is balanced. We are able to see all the details of the face. The blurred background of the building behind the man already starts to disintegrate into the white, but I don’t give it too much importance. When shooting a portrait, all you should care about is the face
Tip 3: Slightly overexpose the face, even if you loose details in the highlights of the background.
The image on the right is obviously overexposed. Look closely at the mans forehead and the nose. Parts of it are completely white, there is no information at all. The structure of the skin disappeared and the color of the skin is gone.
How does exposure works technically?
Imagine your photo sensor as millions of little buckets (instead of pixels) arranged in a rectangle. When no light hits the buckets they stay empty meaning they stay black (= no information). When you shoot your camera and light hits the buckets they are getting filled with information. If a bucket gets completely full it will be completely white (no information again). There is even the effect of overspilling; meaning the filled bucket will overspill and spill over on neighbour buckets turning them into white pixels. Your image will be partly „damaged“ or „burnt“ - what you loose is information and large parts of the image will stay white. You really want to avoid that, but you can’t avoid it always. We are just photographers, not magicians!
How to influence exposure? The exposure triangle.
There is three key settings of a camera called the exposure triangle.
ISO
APERTURE
SHUTTERSPEED
If you think about starting to be a serious photographer, you need to learn how to control these three settings first. How to expose an image correctly depends very much on how you handle the exposure triangle.
The ISO signifies a specified value of your cameras sensor. The sensor is the rectangle surface inside your camera „recording“ the image. In digital photography you can make your sensor more or less sensitive towards light, just by turning a wheel. Small ISO-numbers like ISO 100, ISO 200 indicate that your sensor is not very sensitive towards light. The higher you push your ISO-values (ISO 1600, ISO 3200) the more sensitive the sensor will get towards light. Normally you apply lower numbers in bright sunlight and higher numbers in twilight or inside areas. Side effect: Higher ISO-numbers produce visual noise!
ISO 100 ISO 200 ISO 400 ISO 800 ISO 1600 ISO 3200 ISO 6400
NOTE: If you double the ISO value, you sensor reacts with light twice as fast!
APERTURE. Every lens has aperture blades, which can hinder light passing through once they are closed. You can close them step by step, or open them again, if you want more light to hit your sensor. The steps are given in „f-numbers“. Keep in mind that smaller f-numbers (like f2) mean that the lens is wide open and therefore a lot of light can pass and hit the sensor. Bigger f-numbers (like f22) mean the opposite: the aperture blades are closed, less light will pass the lens! The creative side effect of opening or closing the aperture is what is called depth-of-field. Small f-numbers will have the effect, that only the object in focus is sharp and the background blurs (bookeh). With larger f-numbers you will have over all sharp images. Here the f-numbers in full stops:
f1.4 f2 f2.8 f4 f5.6 f8 f11 f16 f22
NOTE: If you stop down for a full stop (for example f2 > f1.4) double the light will pass through your lens.
Tip 4: Learn these (full) f-stops by hard as they are irregular! There ist f-values in between but only memorise the classic f-stops listed above.
SHUTTER SPEED is the amount of time you let your sensor being exposed. Time is controlled by the shutter curtain, a cloth inside the body of your camera ready to open and close again. You push the shutter release, the sensor gets exposed, the shutter closes again, the picture is taken. In most modern cameras you have exposure times (=shutter speeds) ranging from 1/8000 up to 30“ seconds. Short exposure times allow you to freeze moments. Long exposure times give you the creative opportunity of motion blur. On the other hand long exposure times bring along the unwanted shake blur, in case you shoot handheld in lowlight conditions. The critical area for handheld shots starts with 1/60 or longer, depending on what camera and lens you use. Here typical times from short to long.
1/1000 1/500 1/250 1/125 1/60 1/30 1/15 1/8 1/4 1/2 1“ 2“ ... 30“
NOTE: Half the time means half the light will reach the sensor.
One Exposure, three ways!
Every digital camera is equipped with a light meter that is instructing you how to set up your camera. Let’s make an example. Look at this street scene I shot in Havana.
I‘ve chosen a sensor sensitivity of ISO 400. My light meter proposed me to set my camera on a shutter speed of 1/250 and an aperture of f8. I am accepting these proposals as a time of 1/250 is short enough to shoot handheld and enough depth-of-field (=overall sharpness) for a street scene like this. Now have a look at this table I created.
Depending on what you, the photographer, want to show us, you will choose different settings. In the photo- graph shown above I made a choice, which I thought was appropriate for this scene. If I would have chosen the last of the three options shown in the table, the blue car coming into the frame on the right would shown much more motion blur. Exposure settings always depend on your priorities. If your priority is to freeze action, then you need to set your camera on times of 1/250 and shorter. On the opposite: if you want to indicate motion, then chose longer exposure times. Same with aperture: If you want to isolate your object from your background open the aperture (f1.4, f2, f2.8), if you want high depth-of-field chose higher f-numbers (f8 and beyond). Usually you want to keep ISO-numbers low, as you want to avoid visual noise. With most cameras all values under ISO800 create acceptable noise.
Tip5: Set your ISO first depending on the light, then adjust time and aperture!
Sometimes you will be limited by the light available and reality will force you to opt for a specific setting, sometimes you will have more freedom in making a creative choice. In any case, photography keeps you occupied.
Tip 6: Always know what your intentions are when taking a picture.
Understanding the trinity of ISO, APERTURE and SHUTTER SPEED is the Pater Noster of photography. Once you internalised the exposure triangle you will be able to understand what your camera can do and even more important what it can’t do.
I know, getting into photography can be overwhelming at the beginning, but hey, no-one said it’s gonna be easy. Please trust me when I say, it is totally worth the effort and time. You will understand that owning an expensive camera doesn’t make great pictures in itself. You will know why Ansel Adams was one of the most sophisticated photographers of its time and still outreaches most of todays landscape photographers.
Keep in mind: once you inhaled und understood those rules, you can play with them. But first it is important to understand what your machine is doing once you push gently the shutter. Click!